S-72.227 Digital Communication Systems

1. S-72.227 Digital Communication Systems Fiber-optic Communications - Supplementary

2. G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

3. G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

4. G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

5. G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

6. G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

7. G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

8. G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

9. G. Keiser: Optical Fiber Communications, McGraw-Hill, 2nd Ed.

10. EDFA - energy level diagram Fluoride class level(EDFFA) • Pump power injected at 980 nm causes spontaneous emission from E1 to E3 and there back to E2 • Due to the indicated spontaneous emission lifetimes population inversion (PI) obtained between E1 and E2 • The higher the PI to lower the amplified spontaneous emission (ASE) • Thermalization (distribution of Er3+ atoms) and Stark splitting cause each level to be splitted in class (not a crystal substance) -> a wide band of amplified wavelengths • Practical amplification range 1525 nm - 1570 nm, peak around 1530 nm E4 980 nm excited state absorption E3 Er3+ levels E2 1530 nm 980 nm 1480 nm E1

11. 100 Fundamental limits of silica fibers 50 Water spike 10 5 Band Description Wavelength (nm) 1 Loss (dB/km) O-band Original 1260-1360 E-band Extended 1360-1460 S-band Short 1460-1530 C-band Conventional 1530-1565 L-band Long 1565-1625 U-band Ultra-long 1625-1675 0.5 0.1 Rayleigh scattering Infrared absorption 0.8 1.0 1.2 1.4 1.6 1.8 Wavelength (mm) • C-band: supports early EDFA • C+L-band: support for EDFA’s of today • Raman amplifiers can be used over all bands - new (medium loss) bands are now applicable (as S & U bands) • New fibers can reduce loss at E & S bands (however, EDFA does not work here & Raman gain small) • Inter- and Intra-modal dispersion • Attenuation (Loss) • Non-linear effects • Four-wave mixing (FWM) • Stimulated Raman & Brillouin scattering (SRS,SBS) • Cross-phase & self-phase modulation (SPM,XPM) • Polarization fluctuations

12. Modulation of lasers

13. LD distortion coefficients • Let us assume that an LD transfer curve distortion can be described bywhere x(t) is the modulation current and y(t) is the optical power • n:the order harmonic distortion is described by the distortion coefficientandFor the applied signal we assume and therefore

14. Link calculations • In order to determine repeater spacing on should calculate • power budget • rise-time budget • Optical power loss due to junctions, connectors and fiber • One should be able to estimate required margins with respect of temperature, aging and stability • For rise-time budget one should take into account all the rise times in the link (tx, fiber, rx) • If the link does not fit into specifications • more repeaters • change components • change specifications • Often several design iteration turns are required

15. Link calculations (cont.) • Specifications: transmission distance, data rate (BW), BER • Objectives is then to select • Multimode or single mode fiber: core size, refractive index profile, bandwidth or dispersion, attenuation, numerical aperture or mode-field diameter • LED or laser diode optical source: emission wavelength, spectral line width, output power, effective radiating area, emission pattern, number of emitting modes • PIN or avalanche photodiode: responsivity, operating wavelength, rise time, sensitivity FIBER: SOURCE: DETECTOR/RECEIVER:

16. The bitrate-transmission length grid SI: step index, GI: graded index, MMF: multimode fiber, SMF: single mode fiber

17. Using Mathcad to derive connection between fiber bandwidth and rise time

18. Ref: A.B.Carlson: Communication Systems, 3rd ed

19. Ref: A.B.Carlson: Communication Systems, 3rd ed